1. Field of the Invention
The present invention relates to a novel capsule capable of protecting sensitive active ingredients (e.g., enzymes, peracid bleaches or bleach catalysts). In particular the invention relates to liquid detergent compositions comprising the capsules.
2. Background
It is well known in the art that liquid detergents may provide a hostile environment to sensitive ingredients (e.g., enzymes, peracid bleach, bleach catalysts or perfumes) used in these detergents. For example, enzymes are subject to attack by, anionic actives, high pH conditions and/or by other enzymes. Bleaches, in particular peracid bleaches (such as taught in U.S. Pat. No. 4,909,953 and WO/90,14,336, for example), are known to be particularly harsh on enzyme components. Encapsulation has been used to protect these sensitive ingredients in liquid detergent.
One approach to protecting these sensitive ingredients is to in fact use a polymer shell surrounding the active component to protect the component. This approach has been used, for example, in GB 1,390,503 to Unilever; in EP 266,796 to Showa Denko; and in U.S. Pat. No. 4,777,089 (Lion Corp.).
While such an approach has been effective in protecting active components such as enzyme or enzymes from being attacked by other enzymes or harsh surfactants, this type of capsule does not provide an effective barrier to protect the component from being attacked by bleach. Bleach molecules can penetrate rapidly through the polymer coating and interact with the sensitive ingredient.
In copending patent applications U.S. Ser. Nos. 07/875,872 and 07/875,914, applicants teach an encapsulating polymer system comprising a hydrophilic water soluble polymer or polymers chemically or physically attached to a hydrophobic polymer core particles. Although these applications teach a kind of "web-like" capsule created by the hydrophilic molecules entangling and forming an encapsulating net over the core, this "net" is still too porous to protect the active component, particularly when the liquid composition is a bleach containing liquid composition
Another method which has been used to protect active components from the liquid medium is to place the active in a hydrophobic oil such that the active is protected by the oil from diffusing into the composition where it is subject to degradative attack.
Each of U.S. Pat. No. 4,906,396 to Falholt et al.; EP 356,239 to Allied Colloid; and EP 273,775, for example, provide enzymes protected by hydrophobic oils.
The use of a hydrophobic oil alone, however, does not provide sufficient protection, particularly when the composition also contains powerful degradative components such as the peracid bleaches mentioned above. This may be because the hydrophobic oils were simply not selected carefully enough to deter migration of the degradative components toward the active or, conversely, migration of the active toward the degradative component.
U.S. Pat. No. 4,906,396 to Falholt et al. discloses a detergent enzyme dispersed in a hydrophobic oil. As seen in the examples which follow, the hydrophobic oil is simply incapable of slowing degradation of the enzyme, for example, when placed in a bleach containing liquid composition. Again, whether this is because the hydrophobic oil was not properly selected to sufficiently slow migration of enzyme to bleach or visa versa is unknown. However, the hydrophobic oil alone simply does not function effectively such as the capsules used in the compositions of the subject invention.
In WO 92/20771, Allied Colloids Limited teaches a particulate composition comprising particles having a substantially anhydrous core comprising a matrix polymer containing active ingredient, a layer of hydrophobic oil around the core and a polymer shell around the oil. It is said that the matrix polymer (which contains the active) should be sufficiently hydrophobic that it will partition into the oil rather than the water.
The problem addressed by the patent is that, without the hydrophobic matrix polymer, the active migrates out of the oil too quickly and won't stay in the oil. In other words, the oil layer is incapable of holding a hydrophilic particle without the hydrophobic matrix polymer. Although the retention of a hydrophilic active ingredient by the oil can be enhanced by entrapping the active ingredient with a hydrophobic matrix polymer, this requires modifying the active ingredient with hydrophobic matrix polymer before making the capsule. This in turn both is costly and causes the problem of not rapidly and efficiently releasing the active ingredient in use.
The subject invention differs from the reference in that the oil layer of the capsules used in the subject invention is selected such that it can retain a hydrophilic active in the absence of matrix polymer. Further, as noted above, since the active is not associated with a hydrophobic matrix polymer, it is more readily and efficiently released in use (e.g., when the polymer shell is dissolved).
Accordingly, there is a need in the art for some kind of capsule which can be used in liquid detergent compositions and which can more effectively protect active ingredients, particularly hydrophilic ingredients, from bleaches or other harsh components found in the detergent composition.
Further, there is a need to find such a capsule which also readily and efficiently releases the actives in use, e.g., when the polymeric shell is dissolved or disintegrated in the compositions.